This present disclosure relates to a modular wind turbine system suitable for the construction of wind farms.
The desirability of converting wind energy into electrical energy is well known, namely that the electricity is generated without the burning of fossil fuels, and thus without the associated carbon dioxide emissions.
Conventional wind farms, which consist of large scale horizontal axis turbine installations, suffer from a number of significant financial and environmental drawbacks: each turbine requires its own very tall and heavy steel tower, with extensive electrical cabling run from the turbine hub to the base of each tower and thence to a substation for onward power transmission. Massive tower foundations, new access roads capable of carrying heavy lifting equipment, and additional land drainage are also often required when a conventional wind farm is installed. Apart from the financial, energy and environmental costs of this additional infrastructure, the turbines themselves are often objected to by local communities due to their visual dominance of the landscape and production of visual “flicker” and low frequency noise, which can be perceived as a nuisance even at considerable distances from the installation, due to the height of the turbines above ground level. Environmental objections and physical access for turbine equipment and cranes constitute severe constraints on the range of locations where large onshore wind turbines may be deployed. Offshore wind turbines overcome the visual and noise objections, but suffer even larger installation and cabling/connection costs.
As an alternative to individual large turbines a number of systems have been proposed to mount arrays of smaller turbines on tall towers or large scaffolding-type frames on rotating platforms, in various patents and patent applications, for example U.S. Pat. No. 6,749,399 and W02009130691. These designs, however, would suffer from many or all of the objections described above, particularly cabling costs, noise, and visual obtrusiveness. Additionally, rotating platform devices could require a relatively large footprint on the land they occupy.
A different approach has been to mount smaller turbines on buildings either singly or in arrays as, for example, described in U.S. Pat. No. 4,220,870 and W02005052362. However, a number of studies have shown that the wind speed is so reduced, and turbulence so increased in the vicinity of most buildings, that the energy output of such arrays is likely to be minimal in most cases.
Smaller wind turbines on individual poles placed away from nearby buildings, tall trees or other obstacles produce a much better power output than equivalent building mounted ones. A variety of such machines are now commercially available, including both horizontal axis types, which need to have their rotation axis aligned with the wind direction for optimum efficiency and also “vertical axis” machines which are sometimes described as omnidirectional in that they are able to extract energy with moderate efficiency from wind arriving from any direction in a plane perpendicular to the axis of the turbine. Thus for certain wind directions a “vertical axis” machine will extract energy even if its axis is other than vertical. Conventional installations of individual horizontal or vertical axis machines still require the considerable additional energy, installation and financial costs both of the individual supporting poles or towers, which must be of sufficiently strong construction to withstand gale force winds from any direction, and of the additional electrical cabling or mechanical linkage required to take the power output of each individual turbine from its hub height to ground level and thence to the point of consumption or onward transmission. For low voltage systems, as are commonly used in smaller wind turbines with ratings of 10 kW or less, relatively high electric currents necessarily result when there is significant power output from the generators. Therefore the choice faced by the installer or user is either to invest in large cross-section, and hence expensive, connecting cables from the generator to the point of use or onward transmission, or to accept considerable energy losses due to resistive heating of the cables, if small diameter connecting cables are used.
Some proposals have been made for linear “wind fence” type constructions either at ground level or raised on poles as, for example, described in U.S. Pat. No. 5,642,984, U.S. Pat. No. 4,265,086, U.S. Pat. No. 2,218,867, and U.S. Pat. No. 1,876,595. As with individual turbines on poles, a key problem which arises with such a design is still how to take the energy from where it is harvested by the turbines to where it is to be used. Proposals have included mechanical or hydraulic linkages between the turbines and central power stations or generators, or that turbines have individual electrical generators, the electricity being taken to its point of use or transmission by cables. The use of cabling, hydraulic or mechanical linkages all add considerable cost and complexity to these designs. A second key concern, that of bracing the structure against strong winds, is addressed in some designs by using guy wires attached from the ground to various points on the structure. These would, however, significantly interfere with land use on many farm installations. The conventional alternative, of using individual sufficiently strong vertical poles at intervals implies, as with conventional wind turbines of equivalent swept area, relatively large and heavy poles, and therefore large cranes or similar heavy lifting mechanisms to raise the poles and to raise and attach the turbines to them.
Thus there remains a need for a lightweight and low cost wind farm system which requires minimum materials for its construction, minimizes or eliminates additional access and electrical connection infrastructure, and has minimum environmental impact.